El Niño Watch - Aug 21, 2014

An “El Niño Watch” continues this month as issued by the NOAA Climate Prediction Center several months ago. The watch is just that: we are waiting and watching for the development of a full-fledged El Niño event that has yet to materialize across the equatorial Pacific Ocean. Several indicators of El Nino-Southern Oscillation (ENSO) status declined, moving back towards ENSO-neutral values over the past month instead of leaning towards an El Niño event as they had been. These shifts included slight cooling in the eastern Pacific Ocean and near-average wind patterns along the equator (Figure 1). But for those cheering on the development of an El Niño event, not all hope is lost. A slug of warm water just below the surface has materialized in the western Pacific Ocean and is slowly moving eastward. This is similar to the pulse of warm water that led to dramatic warming in the eastern Pacific Ocean earlier this spring. This “Kelvin Wave” is not as strong in magnitude as the earlier springtime wave, but is expected to surface in the eastern Pacific over the next several months, pouring fuel back into the El Niño engine.

Seasonal ENSO outlooks pick up on this pattern and remain rather bullish in suggesting that an El Niño event is likely later this fall that would peak in early winter (Figure 2). The models suggest this would be a moderate event at best; in fact most models suggest a weak El Niño event of around 1 degree C above average in sea-surface temperatures in the central/eastern Pacific Ocean. The weaker the event, the trickier the forecast with respect to expected precipitation across Arizona and New Mexico. Weak El Niño events vary between wet, near average, and even dry winters in historical records across the Southwest. Official seasonal precipitation forecasts continue to suggest an enhanced chance of above-average precipitation across Arizona and New Mexico through the winter, but confidence in these forecasts is tied to the development and ultimate strength of the El Niño event that has yet to materialize.